Gypsy Moth Silvicultural Experiment Tour

The purpose of this research was to study how
two silvicultural treatments that
reduce stand susceptibility or vulnerability prior to potential gypsy
moth defoliation,
affect gypsy moth dynamics, defoliation, and tree mortality.
The objective of presalvage thinning is to reduce stand vulnerability
through reduction in stand density by removing high hazard trees (i.e.,
those trees which have the highest probability of dying following
defoliation). The trees in the thinned stands can then increase in
vigor and be even more likeley to survive defoliation.
The objective of sanitation thinning is to reduce stand susceptibility,
the likelihood of defoliation, through reducing the highly susceptible
species (mostly oaks) component of the stand and keeping the resistant
and immune components. In this
study, sixteen stands (four pairs of each treatment),
ranging from 19.3 to 31.2 acres and
accounting for a total of 408 acres were selected in 1989. A pair
represents two adjacent stands of similar species composition and size
structure, and reflects comparable suitability as host for the gypsy
moth. One of each pair was thinned in Fall, 1989 or early Spring 1990.
Defoliation followed in six stands in 1990 and in
1991. Each of the six stands incurred over 50% defoliation of preferred
species and over 40% defoliation of all species for two years.
Defoliation on the other stands, i.e. background defoliation level, was
less than 15% of all species, including preferred.

The gypsy moth is known to feed on several hundred different tree
species. Among these species there is considerable variation in
preference and performance. A listing of all tree species and their
relative suitibility for gypsy moth (grouped into 3 catagories) can
be found in
USDA For. Serv. Gen. Tech. Rep. NE 211.
On the West Virginia University forest, where this study was conducted,
most of the preferred tree species were oaks.

Description of the Site

West Virginia University Forest (WVUF) is located in Monongalia and
Preston Counties, West Virginia. This oak-mixed hardwood forest
(ca. 3075 ha) is located 12 km NE of Morgantown along the Chestnut
Ridge anticline, in the Appalachian Plateau physiographic province.
The ridge is underlain by intensely folded rock.
Average elevation of the WVUF is 591 m, but ranges from 318 m to 796 m.
Overstory vegetation varies from stands with a diverse assemblage of
mixed-hardwood species to stands dominated by oak.
Variation in tree-species composition of overstory corresponds
in part to elevation; percentage representation of oak increases
with elevation.

History of the Site

An account of what the site may have looked like at the time of first
European settlement.

"The following day we crossed Chestnut Ridge,
the last of the mountain ranges.
This chain is so named from the immense forests of chestnut trees
that clothe its sides and summit, for nearly the whole of its extent
in Pennsylvania and part of Virginia. The soil is sandy and rocky;
and so exactly adapted to the growth of this tree,
that no part of the world produces it more abundantly.
In fruitful years the hogs from a distance of twenty or thirty miles
were driven by the inhabitants to fatten on its fruit.
Bears, wild turkies (sic), elk and deer traveled from afar to this
nut producing region, and luxuriated on its bountiful crop."

Hildreth, S.P. 1843. Early emigration or the journal of some
emigrant families across the mountains from New England to Muskingum in
1788. American Pioneer 2:112-134

Since the late 18th century the area has been heavily disturbed.
Charcoal manufacture for the iron industry accounted for early use of
the timber resource, followed by specialty wood products such as
railroad ties and whiskey barrels. Nearly all of the Forest was
eventually clearcut and much of it burned by the early 1930's.

Effects of Gypsy Moth Defoliation on Mortality and
Stand Composition

Here is a
table
showing some statistics about each of the 16 stands before and after
thinning.